The field of the present invention is optical scanning of high-resolution color images, and in particular, the use of a flat-bed scanner system for the scanning of reflective and transmissive original documents at high resolution in a high volume production environment typical in the graphic arts electronic prepress industry. The original documents scanned by such systems include color or monochrome photographs, artwork, and composed pages of text and graphics. The actual graphic image content of the scanned original document is referred to as an "original".
In use of a flat-bed scanner for reflective scanning, an original on an opaque substrate is placed with the surface containing the original facing down on a flat transparent reference surface, typically glass. The original document is fixed on the surface such that a single line of the original, herein after referred to as a "scan line" is illuminated from below, and the light reflected from the scan line is directed through an optical system to form an image of the scan line on a sensor such as a CCD array, which converts the optical signal to an electronic representation of the scan line, comprising a line of digital picture elements, or "pixels". The desired portion of the original is scanned, one scan line at a time, by moving the original relative to the illumination system, optical system, and sensor along a direction hereinafter referred to as the "scanning axis". In systems typical of the prior art, such as that disclosed in U.S. Pat. No. 5,341,225, the illumination system, optical system and sensor are configured to move together as a unit. In other systems, such as those of U.S. Pat. No. 5,140,443, the original is moved while the illumination system, optical system and sensor remain fixed. In a production environment, original documents are scanned in a sequence, with each requiring a preparation step in which the original to be scanned is located and fixed on the surface in proper alignment and registration, followed by the actual scanning operation.
A transparent original document, typically a photographic transparency, comprises an original on one side of a thin transparent substrate. In this case, the original is illuminated from the side opposite from that containing the optical system and sensor. Use of a single flat-bed scanner for both types of scanning involves a modal configuration change. Typically, a flipcover used in reflective scanning mode to hold the original document flat on the transparent surface is replaced by a transmissive illumination module which illuminates from above the portion of the original to be scanned. As in reflective-mode scanning, prior art systems are configured so that either the original or one or more scanner illumination, optics or sensor components move to carry out the scanning process.
In addition to reconfiguration of the illumination system, the magnification of the optical system is typically changed so that the same number of pixels imaged on the CCD array, and captured by the digitizing electronics, corresponds to a larger or smaller area of the original. In high-resolution scanning systems typically in use in graphic arts electronic prepress processing, transparencies are oftentimes scanned at resolutions of 2,000 to 4000 pixels per inch (ppi) or greater, while reflective originals are usually scanned at much lower resolutions, for example 600 to 800 ppi. Accordingly, in a production environment in which both reflective and transmissive originals are to be scanned in a mixed processing sequence, mode changes involving illumination system and resolution settings can add significantly to the time required for job processing.
Accordingly, it is an object of the present invention to provide a low cost apparatus for color scanning both reflective and transmissive original documents.
It is another object of the present invention to provide a scanning apparatus with increased scanning efficiency.
It is a further object of the present invention that a single illumination source be used for illuminating both reflective and transmissive original documents.
It is still another object of the present invention to minimize the number of folds in the optical pathway.
It is yet another object of the present invention to provide a scanning apparatus for scanning transmissive original documents at low and high resolution.
Additional objects, advantages, novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description, as well as by practice of the invention. While the invention is described below with reference to preferred embodiment(s), it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of significant utility.